An internal combustion engine for automotive use is known which is equipped with an exhaust gas recirculation system for recirculating exhaust gases from the exhaust system to the air-fuel mixture supply system of the engine at controlled rates. Recirculation of exhaust gases to the mixture supply system is conductive to the reduction of the concentration of noxious nitrogen oxides in the exhaust gases to be discharged from the engine and is, for this reason, effected primarily when the engine is operating under part-throttle or full-throttle conditions.
With a view to assuring stable combustion of combustible charges under idling conditions while achieving reduction of nitrogen oxides in exhaust gases under part-throttle and full-throttle conditions, an internal combustion engine thus equipped with an exhaust gas recirculation system is usually further provided with an intake air bypass system adapted to supply additional air to the engine through a passageway which bypasses the throttle valve in the mixture supply system of the engine during idling conditions when the throttle valve is held in an idling or minimum-open angular position thereof.
In a prior-art internal combustion engine of this type, the exhaust gas recirculation system and the intake air bypass system thus operative are arranged and controlled independently of each other. This has resulted in added complications of the engine construction and has enhanced the severity of the space requirement of the engine.
As alluded to above, however, the intake air bypass system is required to operate under idling conditions alone of the engine while the exhaust gas recirculation system is required to be operative only during part-throttle and full-throttle conditions of the engine. During idling conditions, practically negligible amounts of nitrogen oxides are produced in the combustion chambers of the engine and, therefore, there is no need of recirculating exhaust gases to the mixture supply system. Under part-throttle or full throttle conditions of the engine, the throttle valve in the mixture supply system is held in a wide open or fully open position so that the air to be admixed to fuel in the mixture supply system need not be supplied to the engine through the intake air bypass passageway. Thus, one of the exhaust gas recirculation system and the intake air bypass system is permitted to remain inoperative when the other of the systems remains operative and vice versa.
Attempts have therefore been made to provide an internal combustion engine in which the exhaust gas recirculation system and the intake air bypass system share some operational parts therebetween. Because, however, of the fact that the exhaust recirculation and intake air bypass systems of a conventional internal combustion engine ordinarily uses a vacuum-operated control valve and a solenoid-operated valve controlled by pulse signals, such attempts could not be successfully realized.
The present invention contemplates provision of an internal combustion engine featuring a control system adapted to effectively combine an exhaust gas recirculation system and an intake air bypass system so that both of the systems not only have some operational parts in common but are controlled by one and the same control system.